This invention relates to a thermoplastic elastomer, and more specifically, to a thermoplastic elastomer which has the property of repetitively and reproducibly undergoing crosslinking and de-crosslinking by changing temperature (hereinafter sometimes referred to as “recyclability”).
Recycling of the once used materials is an urgent agenda in these days for environmental protection, resources saving, and other considerations. Crosslinked rubbers (vulcanized rubbers) have stable three dimensional network structure formed by covalent bonding of the macromolecular substance and the crosslinking agent (vulcanizing agent), and accordingly, very high strength. Re-molding of such material, however, is difficult due to the crosslinking by the strong covalent bonding. On the other hand, thermoplastic elastomers utilize physical crosslinking, and molding of such material is readily accomplished by heat melting the material with no complicated vulcanization or molding steps including the premolding.
A typical such thermoplastic elastomer is an thermoplastic elastomer containing a resin component and a rubber component, in which the microcrystalline resin component constitutes the hard segment acting as the crosslinking moiety for the three dimensional network structure thereby preventing plastic deformation of the rubber component (soft segment) at room temperature, and in which the softening or melting of the resin component realizes plastic deformation of the elastomer at an elevated temperature. Such thermoplastic elastomer containing the resin component, however, often suffers from the loss of rubber elasticity, and therefore, a material which can be imparted with thermoplasticity and which is free from such resin component is highly demanded.
In view of such situation, the inventors of the present invention have already proposed that a thermoplastic elastomer which is crosslinkable by hydrogen bond comprising an elastomeric polymer having a carbonyl group-containing group and a heterocyclic amine-containing group in its side chain can repetitively undergo crosslinking and de-crosslinking by changing temperature through the use of the hydrogen bond (see JP 2000-169527 A).
The thermoplastic elastomer having such properties has enormous industrial and environmental value, and such material is also expected as a material having improved higher tensile strength and excellent recyclability with little change in its physical properties even after repetitive crosslinking and de-crosslinking.